The present invention is directed to the use of water sensitive hot melt adhesives for bonding the paper which wraps the filter element of a cigarette and to cigarette filter elements bonded therewith.
A standard filter tipped cigarette is produced by three different operations: (1) filter or plug manufacture, (2) rod manufacture and (3) tipping.
The cigarette rod consists of a stream of tobacco wrapped in a paper tube, the paper tube being glued along one longitudinal edge with a suitable adhesive. This operation takes place at speeds varying from 2,000 to 16,000 cigarettes per minute. The weight of the cigarette rod, diameter, and length are all closely monitored for both cost control and tax reasons.
The filter making operation is similar in many respects to the rod manufacture, but the materials and manufacturing equipment used are different. Tobacco smoke filters are most commonly manufactured from a crimped textile tow of cellulose acetate fibers. The tow is then warmed and rolled to produce a material about 9" wide, and containing an even distribution of fibers. The tow is "bloomed" in a known manner to separate the fibers, and a high boiling solvent, commonly called a "plasticizer", is applied by spraying, wicking, or other suitable means. The treated tow is then pulled into a cylindrical form and wrapped with paper. During an interval of time, which can be accelerated by heating, the plasticizer first partially dissolves the surface of the fibers causing them to become sticky and to bond together at points of contact with each other. The plasticizer then migrates into the fiber leaving the surface dry, but the fibers still remain bonded.
The bloomed tow is then formed into a tube, and wrapped in paper or plugwrap, the paper being glued along one longitudinal edge. Because of the nature of the tow, there is a high degree of radial stress upon the glued bond, so any adhesive used, must be able to stick almost instantly, and hold during storage and use. This has led to the use of hot melt type adhesives, which by formulation are fast setting, and allow very high machine speeds to be used.
Currently polyethylene and ethylene vinyl acetate based hot melt adhesive are used for this filter or plugwrap application. These are preferred since they are relatively non-polar and resist the deteriorous effects of triacetin, the latter being the most commonly used plasticizer which often migrates acting as a solvent for the adhesive causing bond deterioration.
Growing environmental concerns have led to the desire on the part of cigarette manufacturers to develop cigarette filters which will degrade in water over time. Such use requires a hot melt adhesive which will lose strength in water as when flushed or discarded into the environment. The polar nature of such water sensitive hot melt adhesives generally precludes the use of triacetin plasticizers and the cigarette companies, seeking an environmentally friendlier cigarette, are eliminating triacetin in favor of less desirable plasticizers or other filter materials which do not require plasticizers.